(1) Field of the Invention
The present invention relates to a straightening apparatus which straightens a fluid flowing through a pipe having a channel with a large sectional area in the flow of the fluid to prevent the loss of the fluid energy, to reduce noise, and to provide a uniform flow velocity distribution at the outlet of the enlarged channel.
(2) Description of the Prior Art
In design of a diffuser, it is the most important to a fluid while its energy loss in a channel having a large sectional area is minimized. Many studies have been made for diffusers so far, and the design technique of a typical shape is nearly established. For example, according to the results of the Gibson's experiment, a conical diffuser has the relationship between the spread angle 2.theta. of the diffuser and the diffuser efficiency like the one shown in FIG. 1, and the optimal spread angle is 6 to 8.degree. when the sectional area ratio of the channel falls within the range of 2.3 to 9. The optimal spread angle is about 6.degree. in a pyramidal diffuser having a square sectional shape, and about 11.degree. in a two-dimensional diffuser. In this manner, an optimal diffuser shape is designed on the basis of the sectional area ratio of the channel and the diffuser length for each diffuser shape. However, as is apparent from the above example, since the optimal spread angle is very small, a channel having a higher sectional area ratio requires a longer diffuser, resulting in a bulky main body. When the diffuser has a spread angle larger than the above one, a method of inserting a straightening vane in the pipe to divide the channel into channels each having a smaller spread angle is employed. Accordingly, fluid flows along the wall surface of the diffuser and the straightening vane to suppress separation and reduce the energy loss.
In the conventional method, however, a straightening vane having a large spread angle must be arranged in a diffuser having a spread angle much larger than the one shown in FIG. 1. As a consequence, the fluid flows along a surface of the straightening vane and apart from another surface, and the flow velocity distribution greatly varies at the diffuser outlet. If the number of straightening vanes is increased to prevent an increase in spread angle of the straightening vane, the straightening vanes narrow channels to interfere the flow, and the energy loss cannot be reduced.